Eumetazoa

Eumetazoa Temporal range: Ediacaran - Present, 635–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Subkingdom:	Eumetazoa Buetschli, 1910
Subdivisions
Ctenophora †Chancelloriida †Trilobozoa †Proarticulata †Petalonamae ParaHoxozoa Placozoa Planulozoa Cnidaria Bilateria
Synonyms
Enterozoa Lankester, 1877, em. Beklemishev[1][2] Epitheliozoa Ax, 1996 Diploblast Lankester, 1873 Histozoa Ulrich, 1950[3][4]

Eumetazoa (from Ancient Greek εὖ (eû) 'well' μετά (metá) 'after' and ζῷον (zôion) 'animal'), also known as diploblasts, Epitheliozoa or Histozoa, are a proposed basal animal clade as a sister group of Porifera (sponges).^{[5][6][7][8][9]} The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. The competing hypothesis is the Myriazoa clade.^[10]

Several other extinct or obscure life forms, such as Iotuba and Thectardis, appear to have emerged in the group.^[11] Characteristics of eumetazoans include true tissues organized into germ layers, the presence of neurons and muscles, and an embryo that goes through a gastrula stage.

Some phylogenists once speculated the sponges and eumetazoans evolved separately from different single-celled organisms, which would have meant that the animal kingdom does not form a clade (a complete grouping of all organisms descended from a common ancestor). However, genetic studies and some morphological characteristics, like the common presence of choanocytes, now unanimously support a common origin.^[12]

Traditionally, eumetazoans are a major group of animals in the Five Kingdoms classification of Lynn Margulis and K. V. Schwartz, comprising the Radiata and Bilateria – all animals except the sponges.^[13] When treated as a formal taxon Eumetazoa is typically ranked as a subkingdom. The name Metazoa has also been used to refer to this group, but more often refers to the Animalia as a whole. Many classification schemes do not include a subkingdom Eumetazoa.